Almost a Quarter of Texas Ticks Carried a Priority Pathogen

Janis C. Kelly

January 15, 2016

Current surveillance of ticks to predict disease transmission risks occurs mainly in high-risk regions and for established tick-borne pathogens. Researchers now recommended expanding tick surveillance to more low-risk areas as an "early warning" system after they found that 23.3% of 1062 ticks originating in Texas and removed from humans carried Rickettsia, Borrelia, and/or Ehrlichia spp.

Michael S. Allen, PhD, research director, Tick-Borne Disease Research Laboratory, University of North Texas Health Science Center, Fort Worth, and colleagues published their study online January 13 in Emerging Infectious Diseases.

Their analysis was based on data from the Tick-Borne Disease Research Laboratory, which is the primary tick testing facility for Texas Department of State Health Services Zoonosis Control and receives ticks continually throughout the year. The analysis of ticks removed from humans from October 1, 2008, through September 30, 2014, assessed both the prevalence of tick species and the associated tickborne bacterial agents.

Ticks were submitted in individual collection tubes, pulverized for DNA extraction, and screened by polymerase chain reaction for evidence of DNA from Rickettsia, Borrelia, or Ehrlichia spp. Texas Department of State Health Services Zoonosis Control entomologists provided morphologic identification of tick species, and those that could not be classified morphologically were identified by mitochondrial 16S rDNA sequencing.

The testing revealed 13 different tick species, primarily Amblyomma americanum (55.7%). Nearly one quarter of the ticks tested positive for at least one of the three top priority pathogens, most frequently bacteria belonging to spotted group rickettsiae. However, Texas is traditionally considered a region where tickborne infections are relatively infrequent.

Lead author Elizabeth A. Mitchell, also from the University of North Texas Health Science Center, and colleagues write, "We report the detection of known pathogens along with bacteria of unknown pathogenicity in human-parasitizing ticks commonly found in Texas. Our findings underscore the importance of better characterization and continued surveillance of the frequency and distribution of tick species and the bacterial agents they carry. Continued monitoring in low-risk areas provides data regarding the presence of potential emerging pathogens and vectors not yet commonly identified, which could pose unidentified threats to public health."

The project was supported by the State of Texas. The authors have disclosed no relevant financial relationships.

Emerg Infect Dis. Published online January 13, 2016. Full text

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